In the air quality directive (2008/EC/50), the EU has set a target value and a long term objective value for ozone (O3) for the protection of human health. Target value: the maximum daily eight-hour mean may not exceed 120 micrograms per cubic metre (µg/m3) on more than 25 days per calendar year averaged over three years. Long term objective value: the maximum daily eight-hour mean may not exceed 120 micrograms per cubic metre (µg/m3) within a calendar year.